Phase information of the magnetic resonance signal of biological tissue

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Magnetic Resonance (MR) is a non-invasive and versatile technique for imaging and spectroscopy. With MR one can probe biological tissue in various ways, including the investigation of water diffusion, signal relaxation or spectra of cell metabolites. All this information is carried by the signal emitted by atomic nuclei when we manipulate them with magnetic fields. The MR signal can be compared to the beam of a lighthouse. The MR signal strength corresponds to the brightness of the beam. A second aspect of the MR signal is its phase, which corresponds to the direction in which the beam is pointing at a certain time. Usually, only the magnitude is used and the phase is often ignored. However, phase bears a wealth of information. For instance, phase allows the investigation of the spins' magnetic environment, such as tissue magnetic susceptibility. Recent research also showed that the microstructure and the orientation of tissue have an influence on phase. The sources of these frequency shifts, however, are still only poorly understood. The long term objective of the proposed research program is to develop quantitative techniques based on MR signal phase for the investigation of biological tissue. We will investigate how the spatial orientation and the structure of tissue influences the phase. For this we will develop new techniques for MR data acquisition and processing. We will apply these methods to tissues of plants, animals and humans, such as celery, white matter of the brain and spinal cord, and cartilage.